Studies on gas exchange parameters were made at different temperatures and radiation levels in seven seedling populations of chestnut cultivar Judia from different parts of the Trás-os-Montes region, Portugal. Differences were found for the optimal temperature, which was 31°C for JD7, 31.5°C for JD5, 32°C for JD2, 32.5°C for JD4, 33°C for JD3 and JD6, and 33.5°C for JD1 and the ink-resistant hybrid BRO310. At these values, rates of photosynthesis ranged between 8.7 and 13.4 mmol CO
2
m
−2
s
−1
for JD6 and JD7, while the light conditions allowing 90% of maximal photosynthesis varied between 650 (JD6) and 1385 (JD4) μmol m
−2
s
−1
. JD1 showed the highest value of leaf water potential, −0.35 Mpa, and JD6, JD7 and BRO310 the lowest, −0.65 Mpa. JD1 also showed the second lowest stomatal conductance (93 mmol m
−2
s
−1
) and transpiration rate (3.0 mmol H
2
O m
−2
s
−1
).In relation to the photosynthetic pigments, JD3 and JD7 were the most sun-loving clones having the highest values for the Chl
a
/
b
ratio (3.2 and 3.3, respectively), while JD1 had the lowest Chl/Car ratio (3.9). The overall results suggested that the JD3, JD1 and JD5 populations might increase heat stress tolerance in Judia.
Spring Ephemerals Adapt to Extremely High Light Conditions via an Unusual Stabilization of Photosystem II
